The attenuation of gamma (.gamma.) rays from an artificial source can be used to determine the density of a core sample taken from a stratigraphic exploration well. A .gamma.-ray analysis of the core at the wellsite is used in order to make the preliminary selection of portions of the core which are to be further analyzed in a laboratory. Furthermore, preliminary analysis of the core at the drilling site may be useful in guiding the drilling of additional core samples. A system for the wellsite analysis of core samples, for natural .gamma. activity, has been described in U.S. Pat. No. 4,854,163 to Mount, et al. Mount, et al. is directed to an analysis of the natural .gamma. activity of the core sample, which is useful for correlating positions along the core sample with locations within the borehole.
Modern coring technology uses coring techniques in wells which are lined with an inner barrel. These yield core samples which are clad by the barrel. Thus, visual observation of the core quality and of recovery is precluded because the barrel is opaque. (Recovery, the length of core obtained, may be less than the length attempted.) Typically, it is impractical to remove the core from the pipe at the wellsite for such observations. Moreover, barrel-clad core samples are used to obtain core samples in unconsolidated strata. In such strata, the core sample, if not confined by the barrel, would disintegrate into an unstratified mix of the constituent core material, rendering the analysis of the core useless. Such strata are commonly encountered at off-shore wellsites. Therefore, a wellsite analysis system similar to that taught in Mount, et al. may not be usable for the well-site analysis of barrel-liner-clad cores. Thus, in order to access the core within the pipe for analysis, the core sample must be frozen, typically using cryogenic means. The frozen core may then be sectioned for analysis. However, these methods are usually impractical at the wellsite.
Consequently, barrel-clad cores must be transported off site for analysis, which is costly in both time and expense. Or, wellsite analysis relies on simple handheld Geiger counters to preliminarily analyze the cores, a process which is prone to inaccuracy because the Geiger counters are not shielded from background radiation and counts are not energy analyzed Therefore, there is a need in the art for a portable apparatus, and method of using the same, for performing a .gamma.-ray analysis of barrel liner-clad cores.